hdu 1754(基础线段树) I Hate It

http://acm.hdu.edu.cn/showproblem.php?pid=1754

数据比较大,暴力会超时,所以明显是线段树,普通的线段树,结构体中多开一个值sum储存每个子区间的最大成绩,借此更新和查找就行,差不多就是裸的线段树模板

这种基础的要思考透,多按自己的思想修改修改尝试,不然后面的线段树学习会很吃力

code

 #include<cstdio>
 using namespace std;
 struct point {
     int l,r,sum;
 };
 point tree[*];
 int a[];
 int max(int x,int y)
 {
     if (x>y) return x;
     else return y;
 }
 void build(int i,int left,int right)//建树
 {
     tree[i].l=left,tree[i].r=right;
     if (left==right)
     {
         tree[i].sum=a[left];
         return;
     }
     int mid=(left+right)/;
     build(i*,left,mid);
     build(i*+,mid+,right);
     tree[i].sum=max(tree[i*].sum,tree[i*+].sum);
 }
 void update(int i,int pos,int ans)//更新
 {
     if (pos<tree[i].l||tree[i].r<pos)
        return ;
     if (pos==tree[i].l&&tree[i].r==pos)
     {
         tree[i].sum=ans;
         return ;
     }
     int mid=(tree[i].l+tree[i].r)/;
     if (pos<=mid)
        update(i*,pos,ans);
     else
        update(i*+,pos,ans);
     tree[i].sum=max(tree[i*].sum,tree[i*+].sum);
     return ;
 }
 int find(int i,int left,int right)// 查找
 {
     if (left>tree[i].r||right<tree[i].l)
          return ;
     if (left<=tree[i].l&&right>=tree[i].r)
         return tree[i].sum;
     int a=,b=;
     a=find(i*,left,right);
     b=find(i*+,left,right);
     return max(a,b);
 }
 int main()
 {
     int n,m,x,y,i;
     char op;
     while (~scanf("%d %d",&n,&m))
     {
         for (i=;i<=n;i++)
            scanf("%d",&a[i]);
         build(,,n);
         while (m--)
         {
             getchar();
             scanf("%c %d %d",&op,&x,&y);
             if (op=='Q')
             {
                 printf("%d\n",find(,x,y));
             }
             if (op=='U')
             {
                 a[x]=y;
                 update(,x,y);
             }
         }
     }
     return ;
 }